St. Mary Lake is the great east-side lake of Glacier National Park, a long blue trough beneath some of the park's cleanest mountain silhouettes. Going-to-the-Sun Road follows its north shore, so even travellers who never leave the car get repeated views across the water toward rising ridges and hanging valleys. Wild Goose Island, small and improbably placed, is the classic photograph.
The lake feels different from Lake McDonald on the west side. It is windier, more open, and more exposed to the plains, with light that can turn hard and brilliant in the afternoon. Stop at several pullouts rather than treating it as one viewpoint; the shape of the lake changes constantly as the road climbs and bends.